The 2-H-2-oxazolines form a known class of compounds having several members. 2-H-2-Oxazoline is the first member of this series and is the "simplest" molecule. It corresponds to formula I. ##STR1## The 2-H-2-oxazolines and particularly I above are generally quite different from the corresponding 2-substituted-2-oxazolines. This is illustrated by the fact that many conventional processes for preparing 2-substituted-2-oxazolines are not particularly satisfactory for the preparation of the corresponding 2-H-2-oxazolines.
For example, many 2-substituted-2-oxazolines are prepared by dehydrochlorinating a .beta.-chloroalkyl carboxamide with aqueous alkali. However, this process reportedly produced I in only very low yields and was accompanied by decomposition of the desired product. (H. Wenker, J. Am. Chem. Soc., 60, 2152 (1938)).
Another common technique for preparing oxazolines is the cyclodehydration of N-(.beta.-hydroxyalkyl)carboxamides over various catalysts. Litt et al. (U.S. Pat. No. 3,681,329) claim that 2-H-2-oxazolines could be prepared by contacting the appropriate carboxamides with compounds of manganese, cobalt, molybdenum, tungsten and the rare earth metals. Unfortunately, there is no experimental data in Litt et al. which would substantiate this allegation. Hess teaches in Canadian Pat. No. 536,594 and British Pat. No. 758,972 that I can be prepared by a cyclodehydration of N-(.beta.-hydroxyethyl)formamide in the presence of a dehydrating agent (specifically, diatomaceous earth, sulfuric acid, aluminum oxide and iron oxide). The yields were higher than the yield reported by Wenker but were still commercially unsatisfactory.
Eisenbraun (U.S. Pat. No. 3,312,714) teaches the preparation of 2-oxazolines from N-(2-hydroxyethyl)amides using a solid inorganic borate or inorganic salt of a boric acid. 2-Oxazoline yields of from about 63 to 77 percent are reported.
More recently, Ito et al. (J. Am. Chem. Soc., 95:13, 4447 (1973)) reported that 2-H-2-oxazolines and oxazines could be prepared by reacting isonitrile with amino alcohols in the presence of a small amount of silver cyanide. Ito et al. report that I was thus produced in 67 percent yield. Isonitrile and silver cyanide appear to be very unique in this particular reaction.
The chemistry of oxazolines has been reviewed by Wiley et al., Chemical Reviews, Vol. 44, 447-476 (1949), Seeliger et al., Angew. Chem. International Edition, Vol. 5, No. 10, 875-888 (1966), and by Frump, Chemical Reviews, 1971, Vol. 71, No. 5, 483-505. Other references have been classified by the U.S. Patent and Trademark Office under the classification of 260/307F.